Endocrine Abstracts

Background: Bone tissue is a non-classical endocrine organ, which controls phosphate metabolism through production of fibroblast growth factor 23 (FGF-23) mainly by osteocytes. Recent studies have demonstrated that specific proteins involved in paracrine regulation of bone remodeling can be measured in serum samples and may be involved in human metabolism.

Aims: To evaluate serum biomarkers related to endocrine and paracrine function of bone tissue in patients with phosphate metabolism disturbances such as FGF-23 hyperproduction in patients with tumor induced osteomalacia (TIO) or FGF-23 resistance due to acromegaly.

Materials and methods: This is a case-control study. Fasting serum samples were taken between 0800 and1000 h from patients with TIO, acromegaly and age- sex-matched healthy volunteers and stored at −40°C. Commercially available kits for enzyme-linked immunosorbent assay (ELISA) were used to determine the serum levels of iFGF-23 (Biomedica BI-20700), cFGF-23 (Biomedica BI-20702), FGF2 (R&DDFB50), lipocalin (Biovendor RD191102200R) and sclerostin (Biomedica BI-20492). Insulin-like growth factor-1 (IGF-1) was measured by immunochemiluminescence assays (Mediagnost E20). Non-parametric tests (the Kruskal-Wallis test and the Mann-Whitney test) were used to assess the differences between the groups of patients. One-way ANOVA and Bonferroni criterion were utilized to assess the differences between groups.

Results: We enrolled 71 subjects (mean age 48±12 years): 23 patients suffered from TIO (group 1), 24 patients with acromegaly (group 2) and 24 matched healthy controls (group 3) with no differences among the groups in sex and age (P=0.328, 0.959 respectively). Patients with TIO had significantly higher iFGF-23 serum (median 86 [28;736]) and cFGF-23 (5 [3;14]) as compared to the other groups (P=0,003, P<0,001). Phosphorus (Pi) serum levels in subjects with TIO were significantly lower as compared to the other groups (median 0.49 [0.46;0.53] (P<0.001)). Patients with acromegaly had higher Pi - 1.4 [1.3; 1.6] (P<0.001) and IGF1 - 780 [650;810] (P<0.001) vs control. Nevertheless, we did not find statistically significant differences in the measured biomarkers: FGF2 (P=0.38), Lipocalin (P=0.16), sclerostin (P=0.12) within the three investigated groups.

Conclusion: TIO and acromegaly are associated with phosphate metabolism disturbances with no detected changes in the serum levels of FGF2, lipocalin or sclerostin.

Funding 1023022400002-6-3.2.18